1. Field of the Invention
The present invention concerns a homopolar reluctant sensor designed to measure the position of a rotor relative to a stator.
The invention finds a particularly beneficial but not exclusive application in the field of electric motor control.
2. Description of the Prior Art
The Applicant's French patent application No 88 13 272 (now French Pat. No. 2,637,683) describes a device for measuring the angle of rotation of a motor rotor relative to its stator comprising 2n magnetic sensors disposed around a circumference fixed relative to the stator where n is the number of motor phases. Each sensor comprises a magnetic circuit provided with a send coil and a receive coil. The sensors are grouped in pairs in each of which the sensors are offset by 180 electrical degrees. These groups are regularly offset relative to each other by a geometrical angle equal to k/360/2p where k is an arbitrary number and p is the number of motor pole pairs. The send coils are all connected in series and energized by an alternating supply at a frequency between 2 and 15 kHz. The receive coils of the same group of sensors are connected in series. The envelope of the signals at the terminals of said sets of receive coils represents, apart from a phase-shift, the measured angle of rotation of said rotor.
One embodiment of the aforementioned sensor is described in detail in the Applicant's French certificate of addition No 89 10 533.
A sensor of this kind works well but is relatively costly to manufacture, especially in the case of sensors for motors with a small number of poles (less than six poles, for example).
One object of the present invention is to provide a low cost sensor, in particular a sensor for controlling motors with a small number of poles, without compromising the accuracy or reliability of operation.